1. Field of the Invention
The present invention relates to an electron-emitting device, an electron source and an image forming apparatus such as a display apparatus to which the electron-emitting device and the electron source are applied.
2. Related Background Art
There have conventionally known two kinds of electron-emitting devices, such as thermonic cathode and cold-cathode.
The cold-cathode are classified into a field emission type (hereinafter abbreviated as FE type), a metal/insulating layer/metal type (hereinafter abbreviated as MIM type) and so on.
Known as examples of the FE type are those reported by W. P. Dyke and W. W. Dolan, xe2x80x9cField emissionxe2x80x9d Advance in Electron Physics, 8, 89 (1956) and C. A. Spindt, xe2x80x9cPhysical Properties of thin-film field emission cathodes with molybdenum cones,xe2x80x9d J. Appl. Phys., 47, 5248 (1976)
Known as an example of the MIM type is that reported by C. A. Mead, xe2x80x9cOperation of Tunnel-Emission Devices.,xe2x80x9d J. Appl. Phys. 32, 646 (1961).
Examples of the surface conduction type electron-emitting device are disclosed, for example, by Japanese Patent Nos. 2903295 and 2836015. The patent specifications mentioned above disclose device which have been formed may be subjected to a treatment which is referred to as an activation treatment. An. activation treatment step is a step to remarkably vary a device current If and an emission current Ie.
FIGS. 18A and 18B are a plan view and a sectional view of a surface conduction type electron-emitting device such as those disclosed by the specifications mentioned above. In FIGS. 18A and 18B, a reference numeral 1 denotes an insulating substrate, reference numeral 2 and 3 denote electrodes, a reference numeral 4 denotes an electrically conductive film, a reference numeral 5 denotes electron-emitting region, a reference numeral 6 denotes second gaps which are formed by a forming step, a reference numeral 7 denotes a first gap which is formed by the activation treatment step, and a reference numeral 10 denotes carbon films which are formed by the activation treatment step.
Like the forming step, the activation treatment step can be carried out by repeatedly applying a pulse voltage to a device in an atmosphere containing an organic substance. By this treatment, carbon films composed of carbon or a carbon compound is deposited onto at least the electron-emitting region of the device from the organic substance existing in the atmosphere. As a result, the carbon films remarkably varies a device current (If) running between the electrodes 2 and 3 as well as an emission current (Ie) emitted from the electron-emitting region, thereby making it possible to obtain a more favorable electron emission characteristic.
An image forming apparatus can be configured by combining an electron source substrate on which a plurality of such electron-emitting devices are formed with an image forming member composed of a fluorescent substance or the like.
Japanese Patent No. 2630983, Japanese Patent Application Laid-Open No. 10-188854, Japanese Patent Application Laid-Open No. 10-241550, etc. disclose that a glass substrate which is composed, for example, of quartz glass, high silica glass (Vycor), non-alkali glass, borosilicate glass (Pyrex), soda lime glass or soda lime glass laminated with SiO2 is usable as an insulating substrate on which the surface conduction type electron-emitting device is to be formed.
It is considered that a surface of the insulating substrate 1 which is located in the vicinity of the electron-emitting region is heated to a considerably high temperature during the activation treatment of the surface conduction type electron-emitting device and driving of the device.
According to examinations which were made by the applicant of the present application et al., it is estimated that the vicinities of the electron-emitting region in particular are heated to a high temperature on the order of 1000 K during the activation treatment.
Accordingly, at least the surface of the insulating substrate 1 must be free from remarkable variations of physical properties, for example, a variation of the surface due to heat distortion and thermal expansion. Meant by the surface of the insulating substrate 1 is a range which is influenced by the temperature of the electron-emitting region.
From a viewpoint described above, the substrates mentioned above such as quartz glass and high silica glass are usable preferably as the insulating substrate 1. However, these glass materials are expensive and not adequate to manufacture an image forming apparatus or an electron source. Furthermore, it is difficult to facilitate to bond these glass materials with frit glass or the like in an attempt to form a vacuum vessel by using these glass materials.
When a soda lime glass which is inexpensive is used, on the other hand, it reaches a temperature exceeding a strain point at the time of the activation treatment due to temperature rise of the vicinities of the electron-emitting region. The soda lime glass is also expanded remarkably by heat. Therefore, a surface shape of the soda lime glass is remarkably varied.
When a large number of surface conduction type electron-emitting devices are actually formed on soda lime grass, variations of device characteristics caused at the activation step and driving step are remarkable as compared with those which are caused when the electron-emitting device are formed on a quartz substrate. Furthermore, an obtained electron emission characteristic is also low as compared with that when the electron-emitting devices are formed on the quartz substrate.
It is considered that a main reason for this defect is the variation of the surface shape which is caused due to the high temperature produced locally in the vicinity of the electron-emitting region.
That is, it is considered that an effective voltage or electric field applied to the first gap being formed is different from device to device due to the variation of the surface shape of the substrate, thereby causing the variations at the activation step. When a pulse like voltage is applied repeatedly at the activation step in particular, a temperature rise and a temperature drop are recreated as the pulse like voltage is turned on and off. It is therefore assumed that the repeated temperature rise and temperature drop result in difference in shapes of the carbon films and the first gap, thereby causing the variations of electron emission characteristics (If and Ie) obtained at the activation step.
Furthermore, it is considered that the variations caused at the driving step is, like the variations at the activation step, due to the variations with time of the effective voltage or electric field applied to the first gap.
Dependently on a material of the substrate which is in contact with the surface conduction type electron-emitting device, the device characteristics may be varied not only at a manufacturing step but also at the driving step of the devices.
In view of the problems described above, the present invention provides a surface conduction type electron-emitting device which maintains a favorable electron emission characteristic stably for a long time, and an electron source and an image forming apparatus which are inexpensive, and have favorable and highly uniform electron emission characteristics.
Then, the present invention has been achieved on the basis of examinations which were made eagerly to solve the problems described above.
Speaking concretely, the present invention provides an electron-emitting device having a configuration wherein first and second carbon films are formed on a substrate with a first gap interposed, a first and second electrodes are electrically connected to the carbon films respectively, and the substrate disposed at least in the first gap comprises Si, O and N, thereby having a favorable electron emission characteristic which is stable for a long time.
The electron-emitting device according to the present invention is further characterized in that the substrate disposed in the first gap comprises a compound of Si, O and N, and that the compound is oxynitride glass.
Furthermore, the electron-emitting device according to the present invention is characterized in that the substrate is a glass substrate on which a layer of oxynitride glass is formed.
Furthermore, the electron-emitting device according to the present invention is characterized in that the layer of oxynitride glass has a thickness of 1 xcexcm or larger.
Furthermore, the electron-emitting device according to the present invention is characterized in that a layer having a main component of silica is disposed on a surface of the layer composed of oxynitride glass.
Moreover, the electron-emitting device according to the present invention is characterized in that the layer having the main component of silica further comprises phosphorus.
Moreover, the electron-emitting device according to the present invention is characterized in that the layer having the main component of silica has a thickness of 40 nm or larger.
In addition, another embodiment of the present invention is an electron source in which the electron-emitting device described above is disposed in a large number.
In addition, still another embodiment of the present invention is an image forming apparatus which comprises the electron source and an image forming member.
The electron source according to the present invention described above is an electron source which emits electrons in correspondence to an input signal and in which the electron-emitting device according to the present invention is disposed in a plurality on a substrate, preferably characterized in that the electron source comprises a plurality of rows of electron-emitting devices each having ends connected to wiring and a modulation means. More preferably, the electron source according to the present invention is characterized in that arranged on the substrate are a plurality of electron-emitting devices each having a pair of electrodes connected to m wires in an X direction and n wires in a Y direction which are electrically insulated from each other.
Furthermore, the image forming apparatus according to the present invention is an apparatus which forms an image on the basis of an input signal and is characterized by comprising an image forming member and the electron source according to the present invention. By using the image forming apparatus, it is possible to configure a display apparatus for TV broadcasting which comprises an image forming apparatus.
The electron-emitting device according to the present invention which uses the oxynitride glass which has a high thermal stability an a portion of the substrate is capable of suppressing a characteristic of the device from being influenced by a variation of a shape of the substrate due to a temperature rise at both the activation treatment and driving steps described above, thereby maintaining a favorable and stable electron emission characteristic for a long time.
Furthermore, the electron source and image forming apparatus according to the present invention are capable of maintaining stable and high uniformity electron emission characteristic and image displaying characteristic for a long time.